Having owned numerous trikes with varying wheel sizes, I can give my personal impressions.

First, the bigger the rear wheel, the faster the speed for the EXACT SAME chain ring/cassette cog combination. That’s just math and physics but both can achieve the same speeds by shifting gears

Now, since trike builders generally use the same cranksets and cassettes on their machines regardless of wheel size, for the same cadence, the larger rear wheel can achieve a higher top speed and the smaller rear wheel will yield a lower climbing speed.

Second, the small wheel will accelerate faster but the big wheel will “carry” the speed better.

Third, the big wheel will ride softer over bumps and cracks.

Lastly, big rear wheels make for a longer machine so harder to transport.

I currently ride a VTX with a big rear wheel and it rides like a Cadillac but definitely accelerates slower than my small speed trikes and it is long. On my small wheel machines, I mitigate the gearing difference with a larger front chainring.

Finally, average riding speeds are the same regardless of rear wheel size.